CSS text-align: center; is not centering things
I assume you want all the items next to each other, and the whole thing to be centered horizontally.
li elements are display: block by default, taking up all the horizontal space.
Add
div#footer ul li { display: inline }
once you've done that, you probably want to get rid of the list's bullets:
div#footer ul { list-style-type: none; padding: 0px; margin: 0px }
To make a inline-block element align center horizontally in its parent, add text-align:center to its parent.